According to the Weiss theory of ferromagnetism, there is an intimate connection between the specific heat of a body and its magnetisation. Weiss has shown that the magnetic energy per cubic centimetre of a ferromagnetic substance is:- W = -½HI (1) where I is the intensity of magnetisation and H is the molecular field. Further, it is assumed that H = NI (2) where N is a constant depending on the material itself. Thus W = -½NI 2 and d W/ d T = -½N d / d T (I 2 ) where T is the temperature. d W/ d T will contribute to the specific heat of the substance which will become equal to S = s + 1/ρJ d W/ d T, where s = specific heat neglecting magnetic contribution, S = total specific heat, ρ = density, J = mechanical equivalent of heat, Therefore S = s - N/2ρJ d / d T (I 2 ).

On the specific heat of ferromagnetic substances. (1926). Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character, 112(760), 157–176.